This invention relates generally to vehicle mounted aerial devices and more particularly to a platform rotating mechanism which serves to rotate an aerial platform between a position to the side of the boom and a position at the end of the boom.
Vehicle mounted aerial devices have long been used for a variety of applications such as performing work on utility poles and overhead power or telephone lines. The aerial device normally includes a multiple section boom which can either be articulating or extensible and retractable in telescoping fashion. The top end of the upper boom section is equipped with a personnel carrying device which is referred to in the industry as a "platform" and which can be a bucket, basket, stand or similar device. More than one platform or bucket can be provided, and the bucket can be large enough to carry either one or two workers.
It is often desirable to install a material handling jib on the upper boom tip. The jib essentially forms an extension of the upper boom, and it can usually be tilted up or down by a hydraulic cylinder. The material handling jib can be used to handle various materials. One common use is in combination with a hydraulic winch and cable to lift heavy objects such as transformers and the like to the upper end of the boom. In this type of arrangement, the winch cable is passed over a pulley which is carried on the free outer end of the jib.
If a material handling jib is employed, the bucket or buckets must be mounted on the side of the upper boom tip in order to provide room for installation of the jib. If a jib is not used, the bucket can be an end hung bucket mounted on the end of the upper boom. Both the side hung and end hung buckets have certain advantages that are not enjoyed by the other. As previously indicated, the side hung buckets permit the use of a material handling jib. The end hung bucket presents a narrower profile and a more compact arrangement than side hung buckets. Also, the end hung bucket provides more horizontal reach due to its location beyond the end of the upper boom tip.
Devices known as platform rotators have been used with side hung buckets to overcome some of their disadvantages. The platform rotators permit the side hung buckets to be rotated to a limited extent to the front and to the rear from their normal side hung positions. This permits a material handling jib to be used and allows the workers in the buckets to be positioned in various ways to perform various tasks. However, in the platform rotators that have been proposed in the past, the vertical axis about which the bucket rotates is directly or nearly directly in line with the platform pin which mounts the bucket on the upper boom. Due to the location of the vertical axis of rotation in line with or nearly in line with the platform pin axis, the rotation of the buckets is restricted and they cannot swing beyond the end of the upper boom to the position occupied by an end hung bucket. Consequently, side hung buckets have not been able to assume as compact a position as end hung buckets and have not been able to provide as narrow a profile, even when equipped with platform rotators.
In aerial devices having platform rotators, positive leveling systems are used to maintain the bucket in a vertical attitude regardless of the position assumed by the boom assembly. The leveling system most commonly used is a cable and sheave system which acts to maintain a constant orientation of the platform pin on which the platform is mounted. By maintaining the platform pin in a preselected orientation relative to the ground, the floor of the bucket can be maintained in the desired horizontal position at all times as the boom rotates, extends, articulates or pivots up and down. Platform leveling can be achieved with other types of leveling systems such as master and slave cylinders or parallelogram type mechanical linkages. Passive systems which rely on the influence of gravity to maintain the bucket in a vertical orientation can be used on some aerial devices but are inapplicable to the machine of the present invention and other machines having platform rotators.